This invention relates to an LPC (linear predictive coding) analyser and a bandlimiting circuit therefor.
An example of conventional technology employing LPC analysis is described in "Digital Information Compression-Fundamental Technology of INS and VAN Age" by Kazuo Nakada (pp. 90-97, Akiba-Syuppan). FIG. 1 is an explanatory diagram showing how to define frames for analysis as described in this publication. As shown in FIG. 1, input signals are extracted for each analysis frame and auto-correlation functions r.sub.i (i=0 to p) are calculated at an interval t with the following equation (1): ##EQU1## Then, LPC coefficients .alpha..sub.j (j=0 to p) are calculated using the calculated auto-correlation functions r.sub.i, with the following equation (2): ##EQU2##
However, there is a problem in the above-described technology of LPC analysis. Because the relation between the Nyquist rate of the auto-correlation function and the period for calculating the auto-correlation function is not definite, aliasing distortion is added to the auto-correlation function. This may result in LPC coefficients which are discontinuous in time scale especially at a consonant segment of speech signals at which the signal is non-stationary.